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. 2017 Jan;125(1):66-75.
doi: 10.1289/EHP224. Epub 2016 Jun 27.

Delineation of Spatial Variability in the Temperature-Mortality Relationship on Extremely Hot Days in Greater Vancouver, Canada

Hung Chak Ho  1 , Anders Knudby, Blake Byron Walker, Sarah B Henderson
Affiliations

Delineation of Spatial Variability in the Temperature-Mortality Relationship on Extremely Hot Days in Greater Vancouver, Canada

Hung Chak Ho et al. Environ Health Perspect. 2017 Jan.

Abstract

Background: Climate change has increased the frequency and intensity of extremely hot weather. The health risks associated with extemely hot weather are not uniform across affected areas owing to variability in heat exposure and social vulnerability, but these differences are challenging to map with precision.

Objectives: We developed a spatially and temporally stratified case-crossover approach for delineation of areas with higher and lower risks of mortality on extremely hot days and applied this approach in greater Vancouver, Canada.

Methods: Records of all deaths with an extremely hot day as a case day or a control day were extracted from an administrative vital statistics database spanning the years of 1998-2014. Three heat exposure and 11 social vulnerability variables were assigned at the residential location of each decedent. Conditional logistic regression was used to estimate the odds ratio for a 1°C increase in daily mean temperature at a fixed site with an interaction term for decedents living above and below different values of the spatial variables.

Results: The heat exposure and social vulnerability variables with the strongest spatially stratified results were the apparent temperature and the labor nonparticipation rate, respectively. Areas at higher risk had values ≥ 34.4°C for the maximum apparent temperature and ≥ 60% of the population neither employed nor looking for work. These variables were combined in a composite index to quantify their interaction and to enhance visualization of high-risk areas.

Conclusions: Our methods provide a data-driven framework for spatial delineation of the temperature--mortality relationship by heat exposure and social vulnerability. The results can be used to map and target the most vulnerable areas for public health intervention. Citation: Ho HC, Knudby A, Walker BB, Henderson SB. 2017. Delineation of spatial variability in the temperature-mortality relationship on extremely hot days in greater Vancouver, Canada. Environ Health Perspect 125:66-75; http://dx.doi.org/10.1289/EHP224.

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Conflict of interest statement

The authors declare they have no actual or potential competing financial interests.

Figures

Figure 1
Figure 1
The greater Vancouver study area. The map indicates the number of deaths from each census tract that were included in the analytic data set over the entire study period. The base map of this map is the composite of imageries from ArcGIS 10.3.
Figure 2
Figure 2
Illustration of the methods used for the spatial delineation. The left side shows how the split values were defined, and the right side shows how the cut point was identified.
Figure 3
Figure 3
Each figure indicates the odds of mortality associated with a 1°C increase in daily mean humidex (apparent temperature) for decedents who lived in areas above (blue lines) and below (gray lines) each split value on the x-axis. The cut point is marked with a vertical dashed line where applicable, indicating the first statistical separation between 95% confidence intervals. The slope of the above-split relationship after the cut point is shown as a solid black line where applicable. The population and dwelling densities are in units per square kilometer.
Figure 4
Figure 4
Spatial delineation of the composite index using the out-of-hospital mortality subset. Values of the index greater than 37% are classified as higher risk and are shown here by increasing population density (per square kilometer) in order to display the relationship between higher risk and population distribution in the greater Vancouver study area. The base map of this map is the topographic map from ArcGIS 10.3.
Figure 5
Figure 5
The odds of mortality associated with a 1°C increase in daily mean humidex (apparent temperature) for out-of-hospital decedents who lived in areas above (blue lines) and below (gray lines) each split value of the composite index. The cut point is marked with a vertical dashed line, indicating the first statistical separation between 95% confidence intervals. The slope of the above-split relationship after the cut point is shown as a solid black line.
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